This application is based upon Japanese Patent Application Nos. Hei. 11-15573 filed on Jan. 25, 1999, and Hei. 11-304323 filed on Oct. 26, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention:
This invention generally relates to semiconductor physical quantity sensors, and particularly to a semiconductor physical quantity sensor including a beam-structure having a movable electrode for detecting physical quantity such as acceleration, yaw rate, vibration or the like.
2. Related Art:
Conventional semiconductor physical quantity sensor for detecting acceleration, yaw rate, vibration or the like is described in JP-A-9-211022. According to this sensor, abeam-structure having a movable electrode and a fixed electrode confronting with the movable electrode are integrally formed in a semiconductor substrate by processing the semiconductor substrate by using a micro-machine technology. This kind of sensor will be explained in detail hereinafter.
FIG. 83 is a plan view of a semiconductor acceleration sensor. FIGS. 84 to 87 respectively shows sectional views taken along lines 84xe2x80x9484, 85xe2x80x9485, 86xe2x80x9486 and 87xe2x80x9487 in FIG . 83.
In FIGS. 83, 84, a beam-structure 501 ma de of monocrystalline semiconductor material is arranged above an upper surface of a substrate 500. The beam-structure 501 is supported by four anchor portions 502a, 502b, 502c and 502d each of which is protruded from the substrate 500 side, and is arranged with keeping a predetermined distance from the upper surface of the substrate 500. The beam-structure 501 has beam portions 503, 504, a mass portion 505, and comb-shaped movable electrodes 506a to 506d, 507a to 507d. First fixed electrodes 508a to 508d, 509a to 509d, and second fixed electrodes 510a to 510d, 511a to 511d is fixed to the upper surface of the substrate 500. Each of the fixed electrodes 508a to 508d, 509a to 509d, 510a to 510d and 511a to 511d are supported by anchor portions 512 each of which is protruded from the substrate 500 side, and is confronted with each one side of the movable electrodes 506a to 506d, 507a to 507d of the beam-structure 501 arranged with keeping the predetermined distance from the upper surface of the substrate 500. Capacitors are formed between the movable electrodes 506a to 506d, 507a to 507d of the beam-structure 501 and the fixed electrodes 508a to 508d, 509a to 509d. 
As shown in FIG. 84, the substrate 500 has a structure in which a polysilicon thin film 514, a lower layer side insulating thin film 515, a conductive film 516, and an upper layer side insulating thin film 517 are laminated on a silicon substrate 513. As shown in FIG. 83, four wire patterns 518 to 521 are formed by the conductive thin film 516. The wire patterns 518 to 521 are wires of the fixed electrodes 508a to 508d, 510a to 510d, 509a to 509d and 511a to 511d. 
In this structure, degree of acceleration can be detected by measuring displacements of the beam-structure 501 by way of capacitance changes of the capacitors between the movable electrodes and the fixed electrodes, when acceleration is acted on the beam-structure toward a direction parallel to the surface of the substrate.
The acceleration sensor is manufactured as follows. Here, a method of manufacturing will be explained with reference to FIGS. 88 to 97, which are sectional views taken along line 88xe2x80x9488 in FIG. 83.
At first, as shown in FIG. 88, a monocrystalline silicon substrate 530 is provided, and a pattern of trenches 531 is formed in the silicon substrate 530. After that, impurities such as phosphorus are implanted and diffused into the silicon substrate 530 to form electrodes for detecting electrostatic. capacitance. Next, as shown in FIG. 89, a silicon oxide film 532 as a sacrificial layer thin film is formed on the silicon substrate 530, and a surface of the silicon oxide film 532 is flattened. After that, as shown in FIG. 90, a silicon nitride film 534 to be an etching stopper during a sacrificial layer etching is formed. Furthermore, openings 535a to 535c are formed in a laminated structure of the silicon nitride 534 and the silicon oxide film 532 at where anchor portions are to be formed.
Next, as shown in FIG. 91, a polysilicon thin film 536 is formed on the openings 535a to 535c and the silicon nitride film 534. Impurities such as phosphorus are implanted and diffused to the poly silicon thin film 536 to be a conductive film. A wire pattern 536a, a lower electrodes 536b (see FIG. 87) and anchor portions 536c are formed by using a photolithography. As shown in FIG. 92, a silicon oxide film 537 is formed on the polysilicon thin film 536 and the silicon nitride film 534. As shown FIG. 93, a polysilicon thin film 538 as a bonding thin film is formed on a surface of the silicon oxide film 537, and a surface of the polysilicon thin film 538 is mechanically polished to a flat for the purpose of bonding.
Furthermore, as shown in FIG. 94, another monocrystalline silicon substrate 539, which is different from the silicon substrate 530, is provided, and the surface of the polysilicon thin film 538 and the silicon substrate 539 are bonded each other. As shown in FIG. 95, the silicon substrates 530, 539 are reversed, and the silicon substrate 530 side is mechanically polished to a flat. As show in FIG. 96, an interlayer insulating film 540 is formed, and contact holes are formed by dry etching after the photolithography. Furthermore, a silicon nitride film 541 is formed at a predetermined area on the interlayer insulating film 540, and aluminum electrode 542 is formed by depositing and photolithography.
Finally, as shown in FIG. 97, the silicon oxide film 532 is removed by etching using HF-based etchant to make the beam-structure having the movable electrode movable. In other words, the beam-structure 501 and the fixed electrodes (508a, 508b etc) are formed in the silicon substrate 530 by removing a predetermined area of the silicon oxide film 532 by the sacrificial layer etching using the etchant.
In these ways, the semiconductor acceleration sensor using a laminated substrate can be manufactured.
However, in such kinds of semiconductor physical quantity sensor, a sensor structure may be complicated, because it needs to electrically isolate the movable electrode from each of the fixed electrodes from a viewpoint of the sensor structure, and it needs to connect wires with separated electrodes. Furthermore, it is difficult to lower a cost because there is a bonding step of the substrate (the substrate 530 and the substrate 539) as shown in FIG. 94.
This invention has been conceived in view of the background thus far described and its first object is to provide a semiconductor physical quantity sensor having a new electric isolation structure and a method of manufacturing the same.
Its second object is to provide a semiconductor physical quantity sensor, in which a beam-structure having a movable electrode and a fixed electrode confronted with the movable electrode are integrally formed in one substrate, having a new electric isolation structure and a method of manufacturing the same.
According to the present invention, a frame portion, a beam-structure and a fixed electrode are divided. Furthermore, at least one insulator is provided at least one of between the frame portion and the movable electrode, and between the frame portion and the fixed electrode. Therefore, it can easily electrically insulate the frame portion from at least one of the movable electrode and the fixed electrode.
According to another aspect of the present invention, a method comprising:
conducting an anisotropic etching from an upper surface of a semiconductor layer constituting a substrate to form a first trench being vertically extended for electrically insulating a movable electrode and a fixed electrode from a frame portion;
burying an insulator into the first trench;
conducting an another anisotropic etching from the upper surface of the semiconductor layer to form a second trench being vertically extended for dividing and forming the frame portion, a beam-structure, and the fixed electrode;
forming a protection film on a sidewall of the second trench except of a bottom surface thereof; and
conducting an isotropic etching from the bottom surface of the second trench to form a hollow laterally extended for dividing and forming a base plate portion positioned under the hollow, the frame portion positioned as sides of the hollow and the second trench, the beam-structure, and the fixed electrode.
Therefore, it can easily electrically insulate the frame portion from at least one of the movable electrode and the fixed electrode.